1. Field of the Invention
The present invention relates to an apparatus for testing the surface quality of a vessel mouth, especially on a glass vessel. The apparatus is of the type which comprises at least one test head intended to be temporarily mounted on the vessel mouth and which includes a centering piece adapted to be introduced into the vessel mouth, the apparatus is provided with a line which connects the test head to a source of gaseous medium and a pressure measuring appliance which is connected to this line and which generates an electrical signal when a pressure change in excess of a predetermined tolerance value occurs.
In the industrial production of glass vessels, the vessels, formed in a production plant, pass through a final inspection after cooling. In this inspection, those properties in particular of the vessels which are important to their intended use are tested. For the final inspection, automatic mechanical, electrical, pneumatic and optical testing appliances are used, which are combined into a testing sequence or train, commonly known as a sorting line. For the vessels of the type in which the mouth is to be closed airtight by a closure piece, it is necessary especially to test whether the surface of the mouth is sufficiently smooth and plane and is parallel to the bottom surface.
2. Description of the Prior Art
Many devices are already known, by which the quality of a vessel mouth can be tested. In the majority of these devices, a vertically slidable test head is lowered onto the vessel mouth during the test and the vessel is thereby closed. A vacuum or overpressure is then produced in the vessel and, during a predetermined period, it is observed whether the set vacuum or overpressure is maintained. Devices of this type operating with vacuum are described, for example, in Swiss Pat. No. 528,732 and U.S. Pat. No. 2,407,062, while devices operating with overpressure are described in Swiss Pat. No. 556,532 and U.S. Pat. No. 3,496,761. All of these known devices possess an annular seal, which is of a resilient material capable of adjustment and is pressed onto the vessel mouth to carry out the test. The annular seal adapts itself to small chips and depressions of the vessel mouth, with the result that such defects usually cannot be detected. The overpressure used for testing in these known devices is relatively high. This has the disadvantage that a relatively long time is necessary to fill the vessel up to test pressure. Furthermore, when high test pressures are used, the sensitivity of the test procedure is not very high. Finally, in the above-mentioned devices the test head is always rigidly attached to the sliding device, so that even a tolerable slope of the vessel mouth relative to the bottom face causes a fault signal, if it is not compensated by the resilient annular seal.